The present invention relates to methods and compositions for treating subterranean formations. More particularly, the present invention relates to methods and compositions for consolidating particulate matter in a subterranean formation.
Hydrocarbon-producing wells are often stimulated by hydraulic fracturing treatments. Hydraulic fracturing operations generally involve pumping a fracturing fluid into a well bore that penetrates a subterranean formation at a hydraulic pressure sufficient to create or enhance one or more cracks, or “fractures,” in the subterranean formation. “Enhancing” one or more fractures in a subterranean formation, as that term is used herein, is defined to include the extension or enlargement of one or more natural or previously created fractures in the subterranean formation. The fracturing fluid may comprise particulates, often referred to as “proppant particulates,” that are deposited in the fractures. The proppant particulates function, inter alia, to prevent the fractures from fully closing upon the release of hydraulic pressure, forming conductive channels through which fluids may flow to the well bore. After at least one fracture is created and the proppant particulates are substantially in place, the fracturing fluid may be “broken” (i.e., the viscosity of the fluid is reduced), and the fracturing fluid may be recovered from the formation.
Hydrocarbon-producing wells also may undergo gravel packing treatments, inter alia, to reduce the migration of unconsolidated formation particulates into the well bore. In gravel-packing treatments, a treatment fluid suspends particulates (commonly referred to as “gravel particulates”) to be deposited in a desired area in a well bore, e.g., near unconsolidated or weakly consolidated formation zones, to form a gravel pack to enhance sand control. One common type of gravel-packing operation involves placing a sand control screen in the well bore and packing the annulus between the screen and the well bore with the gravel particulates of a specific size designed to prevent the passage of formation sand. The gravel particulates act, inter alia, to prevent the formation particulates from occluding the screen or migrating with the produced hydrocarbons, and the screen acts, inter alia, to prevent the particulates from entering the production tubing. Once the gravel pack is substantially in place, the viscosity of the treatment fluid may be reduced to allow it to be recovered.
In some situations, fracturing and gravel-packing treatments are combined into a single treatment (commonly referred to as “frac-pack” operations). In such “frac-pack” operations, the treatments are generally completed with a gravel pack screen assembly in place with the hydraulic fracturing treatment being pumped through the annular space between the casing and screen. In this situation, the hydraulic fracturing treatment ends in a screen-out condition, creating an annular gravel pack between the screen and casing. In other cases, the fracturing treatment may be performed prior to installing the screen and placing a gravel pack.
Occasionally, sand, gravel, proppant, and/or other unconsolidated particulates placed in the subterranean formation during a fracturing, gravel packing, or frac-pack operation may migrate out of the subterranean formation into a well bore and/or may be produced with the oil, gas, water, and/or other fluids produced by the well. The presence of such particulates, in produced fluids is undesirable in that the particulates may abrade pumping and other producing equipment and/or reduce the production of desired fluids from the well. Moreover, particulates that have migrated into a well bore (e.g., inside the casing and/or perforations in a cased hole), among other things, may clog portions of the well bore, hindering the production of desired fluids from the well. The term “unconsolidated particulates,” and derivatives thereof, is defined herein to include loose particulates and particulates bonded with insufficient bond strength to withstand the forces created by the production of fluids through the formation. Unconsolidated particulates may comprise, among other things, sand, gravel, fines and/or proppant particulates in the subterranean formation.
One method of controlling unconsolidated particulates has been to produce fluids from the formations at low flow rates. The production of unconsolidated particulates may still occur, however, due to unintentionally high production rates and/or pressure cycling as may occur from repeated shut-ins and start ups of a well. Moreover, producing fluids from the formations at low flow rates may prove economically inefficient or unfeasible.
Another technique used to control unconsolidated particulates has been to coat the particulates with a tackifying agent or curable resin prior to their introduction into the subterranean formation and allowing the tackifying agent or resin to consolidate the particulates once inside the formation. In general, the tackifying agent or resin enhances the grain-to-grain, or grain-to-formation, contact between particulates and/or subterranean formation so that the particulates are stabilized, locked in place, or at least partially immobilized such that they are resistant to flowing with produced or injected fluids.
Yet another technique used to control particulates in unconsolidated formations involves application of a consolidation fluid containing resins or tackifying agents to consolidate particulates into a stable, permeable mass after their placement in the subterranean formation. These consolidation fluids may be preferentially placed in a particular region of a subterranean formation using isolation tools, such as “pack off” devices, packers, gel plugs, mechanical plugs, bridge plugs, ball sealers, and the like.